The goal of this project is to characterize a novel gene at 1511-13 termed BCL8, which rearranges with the IGH gene in DLLC. The following Specific Aims are proposed. 1. Genomic and cDNA organization and predicted protein of BCL8. The gene is expressed in multiple tissues, notably in nonlymphoid tissues such as prostate and testis. Using a testis cDNA library, we have cloned BCL8 cDNA. We will now determine the genomic and cDNA organization of BCL8 and develop antisera against the predicted protein suitable for detecting gene expression by Western blotting and immunohistochemistry. 2. Mechanism of BCL8 deregulation in DLLC. We will determine the consequence of chromosome translocation to BCL8 deregulation in DLLC. By Northern blot analysis, we will determine the frequency and level of BCL8 expression in B-cell DLLC and its correlation with BCL8 rearrangements. We will also investigate if additional mechanisms of deregulation, such as mutations or deletions n the 5' regulatory region operate. By conventional genomic cloning using BCL8 probes and 3' and 5' and 3' RACE (rapid amplification of cDNA ends) techniques, we will identify sequences from tanslocation junctions involving BCL8 with chromosomal sites other than 14q32. Such analysis will clarify the mechanism(s) and consequence of promiscuous translocations affecting BCL8. 3. Role of BCL8 in normal and lymphoid tumor development. We will investigate the role of aberrant BCL8 expression in lymphoid tumor development. Expression vectors containing BCL8 gene will be transfected into EBV- immortalized B-lymphoblastoid cell lines. Expression vectors containing the BCL8 gene under the regulation of IG-gene enhancer will be used to construct transgenic mice to overexpress of the transgene in B-cell lineage. These studies will elucidate the role of BCL-8 in normal development and lymphoid neoplasia.